Production of magnesium



Jan. 8, 1952 F. J. HANSGIRG 2,582,120

PRODUCTION oF MAGNESIUM' OrignalvFiled Sept. 24, 1946 2 SHEETS-SHEET l ATTORNEYS Jan. 8, 1952 F. J. HANSGIRG PRODUCTION 0F MAGNESIUM original Filed sept. 24, 1946 2 SHEETS- SHEET v2 4 ,Z2/Wr j( vif-Jaar ATTORNEY? Patented Jan. 8, 1952 'UNITED STATT:

s PATENT oFF 2,582,120 IC E PRODUCTION oF MAGNESIUM Original application September 24, 1946, Serial No. 698,984. Divided and this application December 17, 1948, Serial No. `65,855

2 Claims.

MgO-i-CSMg +CO From this highly reversible reaction, magnesium can be recovered only if the gaseous products of reactionmagnesium vapor and carbon monoxide--which are stable at 2000 C., are suddenly cooled to about 200 C., at which temperature the reaction of the magnesium on carbon monoxide is slow enough to ensure that back reaction is prevented. For effecting this shock cooling, different methods have been proposed; for example, the admixture of inert gases with the hot products of reaction at the moment they are discharged from the reduction chamber. For this purpose, hydrogen, hydro-carbon gases, or inert gases like argon have been proposed. Also sprays of liquids such as hydro-carbons or liquid metals such as lead or tin, have been suggested. Finally, even the introduction of solid sprays has been proposed-as for example, mixtures of hydrogen and solid powders of magnesium chloride-to make use of the cooling eect of the heat of fusion.

All of these methods have been partially successful but in every case there have been certain disadvantages. In chilling with hydrogen, it is necessary to recover the admixed carbon monoxide from the hydrogen gas for the purpose of recycling the hydrogen into the process. The chilling with hydrocarbons has the disadvantage that some decomposition takes place and the magnesium dust so recovered is contaminated by excess carbon and also by absorbed heavy gases which makes it difficult to briquette such dust for 'the final operation. The metallic sprays also give incomplete protection against back reaction and it is difficult to recover the magnesium from the alloys so formed.

One prior proposal suggests rst cooling the gaseous magnesium and carbon monoxide down to the dew point by means of a cool inert gas, and then eifecting further cooling and the condensation of the magnesium by contact with a slowly moving cold surface. This method is ineffective to produce any satisfactory yield of magnesium since the speed of back-reaction is so fast 2 that at the dew point (about 1150D C.) a greater part of the magnesium will be reconverted into magnesium oxide and carbon.

The applicant has found that the chilling of the gases must ybe effected within a period of from 1/woo to 1/sooo of a second and must proceed down to a point approximating 250 C. before it can be said that the losses by back-reaction are negligible. If by the fastest methods of-'gas cooling, the mixture is brought down to about 660 C., some magnesium can be condensed but a yield of more than of magnesium cannot lbe expected, and the particles of magnesium recovered will be coated with the back-reacted material, magnesium oxide and carbon.

It is therefore the purpose of the present invention to provide means and methods for shock cooling or chilling a body of gaseous magnesium and carbon monoxide upon a cold surface at a high speed of contact. The applicant has determined experimentally that the heat transfer between the gases coming out of the furnace at comparatively low speed is not great enough to effect the shock cooling with a velocity which is greater than the velocity of the back reaction. It is known that the heat transfer coeflicient between a gas and a solid surface increases nearly proportionately to the velocity of the gas against such surface. It is therefore possible to effect a shock cooling with high enough speed, if the gaseous products of reaction between the magnesium oxide and the carbon are carried along a water cooled metallic surface with a very high velocity. To so discharge the gas against a stationary cooled surface would, of course, require that a high pressure be maintained in the reduction furnace. Such procedure would be impractical since it is already difficult enough to maintain an electric reduction furnace gastight in operation at high temperatures with yonly a slight over-pressure against the outside atmospheric pressure.

It `is therefore the aim of the present invention to effect the shock cooling of the gases on rapidly moving water-cooled chilling surfaces, where the heat will be transferred from the gaseous products of reaction to these cooling surfaces ,in a very short time. It is preferred that the zone of contact be rather shallow and in practice it may comprise a narrow clearance space between confining surfaces having a high rate of relative velocity, one or both of said surfaces being cooled. At the same time, by a proper arrangement of apparatus, the dust containing the metallic magnesium is immediately moved from the cooled surface upon which it condenses, so that a clean surface is always eX- posed to new mixtures of magnesium vapor and carbon monoxide. To aid in preventing any subsequent action of carbon monoxide in high concent1-ation, if desired, a quantity of protective gas may be introduced at the same time; but the amount to be used is so much smaller in this case than in prior processes, since it is neither necessary nor possible to remove all of the heat from the gaseous products of reaction in the extremely short period of time allowed, merely by admixing therewith a cooled gas to lower the temperature of the total gas volume according to the laws of gaseous mixtures.

Other objects and features of novelty will be apparent from the following specification when read in connection with the accompanying drawings in which one embodiment of the invention is illustrated by Way of example.

In the drawings,

Figure l is a diagrammatic view in vertical section of a reduction furnace, showing the shock cooling installation chiefly in elevation;

'Figure 1A is a diagrammatic top plan view on a much reduced scale, of the furnace shown in Figure l;

Figure 2 is aview in vertical section of the shock cooling arrangement; and

Figure 3 is a cross-sectional view through the reamer head for cleaning the furnace discharge opening."

In Figure l of the drawings, the reduction furnace, wherein the magnesium oxide and carbon are converted into magnesium vapor and carbon monoxide, is designated generally by the reference numeral I3. The furnace may be built up of carbon blocks and arches in the usual sway, and jacketed with an airtight covering of sheet metal. The Crucible chamber of the furnace is indicated at II and it will be seen that an electrode I2 enters the chamber through an opening I3, the opening being sealed around the electrode by means of a water-cooled airtight gland indicated diagrarnmatically at I4. The reduction furnace is charged through the feeder tube I5 which is also sealed off by means of a suitable gland as indicated at I5. According to the usual practice a bed of hot granulated coke or carbon dust is formed in the chamber II in which the electrode I2 is immersed. The briquetted raw material is introduced through the feeder tube I5 and it gasies immediately. The magnesium vapors and carbon monoxide resulting from the reduction reaction leave the furnace through the opening in the side wall thereof.

The shock cooling installation is disposed closely adjacent the furnace, and in the present illustrated embodiment is indeed housed Within the confines of the exterior wall of the furnace itself. Within this furnace Wall there is formed a relatively narrow verticaly `disposed chamber 22 which iswell insulated from the combustion or reaction chamber Il of the furnace. The charnber 22 extends downwardly below the level of lthe combustion chamber and terminates in a trough 23. Any suitable discharge means for the material resulting from the shock cooling of the gases may be provided within the trough 23, for example, the screw conveyor` 24.

Within the cooling chamber `22, and preferably against the inner wall thereof is disposed a hollow metallic box 25 which may be of disclike configuration andwhich has a central opening 2E therein forming a continuation of the discharge opening 2d from the furnace proper. The hO'llOW interior Space 2 of 'the box 25 is provided withpipes 28 and 29 for the introduction of gas inert to magnesium for the purpose of diluting the reacting gases and furnishing incidental cooling. A multiplicity of openings 30 are provided in the outer face of this box 25 so as to discharge this gas into the cooling chamber'.

Facing the disc like box or hollow wall 25 is a similar hollow disc .32, the face of this disc lying rather close to the perforated face of the disc 25 to provide a narrow space between these surfaces for the reaction gases. In the case of a furnace of the capacity of say one-half metric ton of magnesiumrper hour and which produces a gas quantum of Aabout 2.2 cubic meters per second measured at 2000 C., the discs may well be of the order of from four to six and one-half feet in diameter and the clearance space approximately one inch wide. However, these approximations may be varied and, of course, some of them would necessarily vchange with variations in the size of the furnace installation. The hollow disc or plate 32 is mounted to rotate within the chamber 22 about a horizontal axis which preferably coincides with the axis of the opening 20. The disc 32 is carried by or forms an integral part of the rotatable hollow shaft 35, which rotates in the water or oil cooled gland bearing 36 in the outer wall portion of the furnace I0. Any other bearing supports which shall be found necessary may be provided for the outer portions of the hollow shaft 35. In order to drive the shaft a sprocket such as that indicated at 38 may be fixed upon the shaft and the device may be connected to a motor or other suitable source of power as by means of the drive chain 39.

Cooling fluid is led to and from the hollow interior 45 o'f the disc 32 through the passageways 4I and 42, the former receiving fluid from the intake header ring 43 and the latter discharging into the similarly formed ring 44 which surrounds the shaft 35. These header or manifold rings are held stationary and are provided respectively with intake and outlet pipes 43 and 45. Sealing glands or rings 46 are provided to prevent leakage during the rotation of the shaft. An axially disposed reamer or scraper head 50 is disposed for movement axially of the shaft 35 so that it may be periodically projected into the discharge opening 26 of the furnace in order to keep the opening clean. The reamer head 5I] is cruciform in cross section as indicated in Figure 3 of the drawings. This reamer head is cooled by Water or oil supplied through the central hollow pipe or shaft 5I in which is centered a tube 52. This tube 52 is received within a non-rotatable head 53 which is supplied with cooling liquid through the pipe 54. rIhe hollow reamer shaft 5I passes through a packed supporting block 55 carried within the hollow interior chamber 56 of the rotating shaft 35. Fixed to the reamer shaft 5I at' a point to the right of its center as viewed in Figure '2 is a piston member 5S which fits within the cylindrical inner chamber 51 provided upon the right hand side of the central plug or block 55. Between the block 55 and the piston 56 there is disposed a coil compression spring 58 which urges the reamer toward its retracted position. A duct 59 leads from the chamber 51, upon the right hand side of the piston 56, to a hollow stationary ring 60 which surrounds the shaft 35 and is sealed thereagainst by means of the gland or packing 6I. The head 60 is provided with a pipe connection 62 through which pressure uid may be introduced or withdrawn. When pressure fluid is introduced to the ring 60 and the chamber 51, the piston 56 is moved toward the left and forces the reamer head 50 toward the opening 20, 26 and thus cleans out any deposits which may have accumulated in the opening. The cross shaped configuration of the reamer head permits the furnace gases to discharge through the opening even when the reamer is inserted therein. The operation of the hydraulically moved reamer may be effected either at will or automatically and periodically. For example the admission and discharge of pressure fluid through the pipe 62 may be controlled by suitable well-known clock-work or timing control mechanism, suggested at 62A in Figure 1.

In operation the gases discharged through the openings 20, 26 pass into the at narrow space 65 between the adjacent surfaces of the stationary disc 25 and the rotating disc 32. The disc 32 is preferably rotated at a rather high velocity and thus a very rapid speed of contact between the gases and the cooling disc is effected.

The applicant has determined that the relative velocity of the gases to be chilled, with respect to the chilling surface should be from about 150 to about 1000 feet per second. This suggests a speed of the disc 32 and shaft 35 of approximately 1200 R. P. M. in the case of an installation of the approximate dimensions and capacity mentioned above. Below the lower limit stated, there is too great danger of the occurrence of back-reaction, and the upper limit suggested while not critical indicates the probable point of uneconomical operation or mechanical inexpediency. Preferably, at the same time that the surface cooling of the gases is being accomplished, jets of cooled hydrogen, natural gas, or other gases inert to magnesium are discharged through the openings 30 in the outer surface of the stationary disc 25. For a maximum yield the carbon monoxide concentration should not be higher than about 30% of the gas with which the magnesium dust remains in contact for the time necessary to separate it from the gas stream and the primary purpose of the injection of this diluent gas is to keep the carbon monoxide concentration down to this figure. It should be thoroughly understood that the amount of diluent gas supplied for this purpose is far less than that which would be required of itself to effectuate the cooling of the reaction gases from approximately 2000 C. to the neighborhood of 250 C. without back-reaction. It may be mentioned that if such an amount of diluent gas were to be used, it would result in a final carbon monoxide concentration of only 3%, and it will thus be observed that with the present process the amount of diluent gas used may be reduced even down to one tenth of that required to effect the shock cooling alone.

The effect of the rapid surface cooling, and especially as employed in conjunction with the diluent inert gas, is to greatly improve the recovery of magnesium from any of the carbothermal reduction processes.

It is understood that various changes and modiiications may be made in the apparatus and procedures illustrated and described herein without departing from the scope of the invention as defined by the sub-joined claims. For example, the chilling member might be one having a cooled surface moving rectilinearly instead of rotatively in contact with the stream of gases at the high relative velocity required.

Within the context of this application, the phrase "relative velocity is to be understood to signify the algebraic difference of the velocity of the gases and that of the moving surface. In other words, if the gases are moving in the same direction as the surface the respective velocities are subtracted, but if they are moving in the opposite direction to that of the moving surface the velocities are added. By contact velocty" is meant the instantaneous relative velocity at any point of impingement of the gaseous stream upon the cooled moving surface.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A process for producing metallic magnesium by the thermal reduction of materials containing magnesium oxide by means of carbon, which includes shock-cooling the hot gaseous products of the reduction reaction as they issue from the furnace, down to a temperature of less than 250 C., by moving said gases in the form of a thin flat sheet between closely spaced parallel surfaces, cooling at least one of said surfaces, maintaining both surfaces in a dry condition, and maintaining said cooledsurface in such a state of rapid rotation in its own plane and parallel to the plane of the other surface, as to eiect a relative contact velocity of the gases with respect to the rotating chilling surface of not less than approximately feet per second.

2. A process for producing metallic magnesium by the thermal reduction of materials containing magnesium oxide by means of carbon, which includes shock-cooling the hot gaseous products of the reduction reaction as they issue from the furnace, down to a temperature of less than 250 C., by moving said gases in the form of a thin flat sheet between closely spaced parallel surfaces, cooling at least one of said surfaces, maintaining both surfaces in a dry condition, maintaining the cooled surface in such a state of rapid rotation in its own plane and parallel to the plane of the other surface, as to effect a relative contact velocity of the gases with respect to the rotating chilling surface of not less than approximately 150 feet per second, introducing a diluent gas into the moving sheet of gaseous products directly at the zone of contact at the very point of impingement of the sheet upon said surface for admixture with said gaseous products simultaneously with the chilling action of the moving surface, the amount of such diluent gas being much less than that which could alone effect the cooling the reduction products without back-reaction, said quantity of diluent gas being no more than that necessary to keep the carbon monoxide concentration no higher than 30% of the gas with which the condensed magnesium dust remains in contact for the time necessary to separate it from the gas stream, and finally separating the magnesium dust from the gas stream.

FRITZ J. HANSGIRG.

REFERENCES CITED The following references are of record in the nle of this patent:

UNITED STATES PATENTS Number Name Date 2,018,265 Kemmer Oct. 22, 1935 2,238,908 McConica, 3rd Apr. 22, 1941 2,391,727 McConica, 3rd Dec. 25, 1945 

1. A PROCESS FOR PRODUCING METALLIC MAGNESIUM BY THE THERMAL REDUCTION OF MATERIALS CONTAINING MAGNESIUM OXIDE BY MEANS OF CARBON, WHICH INCLUDES SHOCK-COOLING THE HOT GASEOUS PRODUCTS OF THE REDUCTION REACTION AS THEY ISSUE FROM THE FURNACE, DOWN TO A TEMPERATURE OF LESS THAN 250* C. BY MOVING SAID GASES IN THE FORM OF A THIN FLAT SHEET BETWEEN CLOSELY SPACED PARALLEL SURFACES, COOLING AT LEAST ONE OF SAID SURFACES, MAINTAINING BOTH SURFACES IN A DRY CONDITION, AND MAINTAINING SAID COOLED SURFACE IN SUCH A STATE OF RAPID ROTATION IN ITS OWN PLANE AND PARALLEL TO THE PLANE OF THE OTHER SURFACE, AS TO EFFECT A RELATIVE CONTACT VELOCITY OF THE GASES WITH RESPECT TO THE ROTATING CHILLING SURFACE OF NOT LESS THAN APPROZIMATELY 150 FEET PER SECOND. 